A conventional medical image diagnostic apparatus, such as an X-ray angiography apparatus, generates three-dimensional image data (hereinafter, also referred to as “volume data”). Based on the generated volume data, various examinations and diagnoses are carried out. For example, the volume data generated by the medical image diagnostic apparatus is converted into a two-dimensional image that reflects the three-dimensional information through volume rendering processing, and the two-dimensional image is displayed on a monitor. An observer (such as a doctor who performs manipulative operations using an X-ray angiography apparatus) performs various examinations, diagnoses, and treatments while observing the two-dimensional image displayed on the monitor.
In the above-described volume rendering processing, an arbitrary point of view with respect to a site that is a subject of examination, diagnosis, or treatment is defined and a projection surface for projecting, as a two-dimensional image, the three-dimensional volume data from the defined point of view and a line of sight from the defined point of view toward the projection surface are defined. The gradation levels of the pixels on the projection surface are then determined based on the voxel values on the light of sight from the point of view toward the projection surface. When the gradation levels on the projection surface are determined, setting an opacity for each voxel value determines the display mode of the subject site viewed from the arbitrary point of view. In other words, a setting is made about how the defined line of sight is transmitted through the subject site and on how the line of sight reflects when the projection surface is viewed from the defined point of view. The opacity is properly adjusted in order for, for example, an easy-to-see display of the site to be measured (observed).
Furthermore, as such a system applied to the X-ray angiography apparatus, a system is known where the X-ray angiography apparatus operated by an operator (such as medical technologist) who is in operation room according to an instruction from a doctor who is in examination room. The system, if it is a simple operation, can be operated by a user terminal in hand of the doctor. With the development of the user terminal (such as tablet device) can also be used for medical, the doctor has enabled more complex operations by the user terminal are disposed on hand of the doctor. With the above-described conventional technology, it may be difficult to make an easy-to-see display of a site to be observed by the doctor performs operations.